How do you test the fuel guage sending unit???

My wife's does that too-the needle stays above full until it's almost empty. When the needle finally drops, it's time to get to a gas station fast. I've had this happen in every Ford I've owned (5 of them) and it was always the sending unit. Not saying that's it, but I don't know how to test it other than pulling it out, at which point you may as well put in a new one. It may well be the gauge, Ford gauges suck in these cars, but I've never had a fuel gauge go yet.

All the sending unit is, is a rheostat that has a variable resistor wiper contact and an arm with multiple cotact needles. They wear over time and/or get brittle and break, so the point where it rides the most loses it's reading via the gauge first. I forget how fords go but you can splice into or disconnect the return from the sender to the gauge and put it to ground or supply 12 volts. If you get an empty reading then it's the sender (usually is anyway). Or if you have too many gizmos you can connect a potentiometer to it and watch the gauge work the way it is supposed to with varrying the resistance.

Anyway, replace the fuel level sending unit.